A transpiration estimation model for complete vegetation and an evaporation estimation model for bare soil are presented, based on information of surface parameters. Combined with vegetation coverage data, a model for regional evapotranspiration (ET) estimation over the heterogeneous landscape is derived. This approach provided a reliable estimate of ET over Northwest China, the semiarid and arid region of China. The accuracy of the model for regional ET estimation is checked, which shows a high accuracy result. The features of ET over Northwest China are also discussed with the model